In recent years, an active-matrix-type liquid crystal display is widely used. The active-matrix-type liquid crystal display has a thin film transistor (TFT) as a switching device for each pixel.
An amorphous-silicon-type thin film transistor having an active layer formed of amorphous silicon is known as the thin film transistor, in addition to a polysilicon-type thin film transistor having an active layer formed of polysilicon (see Patent Document 1).
The amorphous-silicon-type thin film transistor has an advantage that it can be uniformly deposited on a substrate having a relatively large area because an active layer can be produced more easily in the amorphous-silicon-type thin film transistor than in the polysilicon-type thin film transistor. However, since the amorphous-silicon-type thin film transistor has carrier mobility lower than that of the polysilicon-type thin film transistor, it has been difficult to produce a higher-definition display.
On the other hand, there is known a technique in which a channel portion of an active layer, which is located between a source electrode and a drain electrode, is crystallized by laser annealing to thereby improve carrier mobility. For example, Patent Document 1 discloses a method of producing a semiconductor device in which an active layer is modified using a KrF excimer laser (wavelength of 248 nm) to improve mobility.
Patent Document 1: Japanese Patent Application Laid-open No. Hei 10-56180 (Paragraph [0110])